I am the guy who asked about non-toxic "homebrew" formulas for cleaning built up carbon deposits - inside the neck of brass. I am a novice hand loader so I have lots left to learn
I inherited some older , well used brass that might be "work hardened" = varying degrees of brittleness, the carbon buildup appears to be almost "baked on" after many uses. "Work hardening" can also occur when brass is set back to the original factory COL with a full length die set after every use, when fired in a long throat / freebore chamber = lots of stretching. Some guys trim brass length back to factory COL after every use - the wall thickness of the neck gets thinner after each trim, because of stretching. Small cracks can appear on work hardened brass during shooting, resizing and seating - visual inspection should be done , after each step. Easier to observe small cracks from the inside of brass with a clean neck. There is a potential for the carbon buildup of crud to fill a hairline crack from the inside, when the bullet is seated. It wouldn't be visible until the crack reaches the outside of the neck. One guy on a forum used a hawkeye boroscope on 308 brass and he estimated .2 grains of capacity was lost on the inside with well baked on carbon crud. It doesn't seem like a lot but for one who works up to a maximum load , that may result in a stiff bolt lift due to a potential overpressure. Brass that weighs significantly more often requires reduced powder loads. Norma mentions in their hand load book , 300wm - two different production runs : one for heavier brass with less volume and lighter brass with more volume. Powder loads are different for the heavier (270gr) and lighter brass(215gr) !!!
https://gundigest.com/more/how-to/br...breaking-point
Usually you will find that when a cartridge has become too brittle to withstand that reworking, it will develop a hairline crack in the case mouth, either at the edge of the case mouth, or just below it.
Some guys mention on other forums - they use ultra sonic cleaners or ss pins = brass comes out sparkling clean inside / out, seating bullets become very smooth and consistent. A cleaner inside neck may lower the possibility of bullet runout during seating.
